Broadly speaking, the invention relates to open-system interconnection environments as is shown in the attached FIG. 4. The term "open-system interconnection (OSI)t" qualifies standards for the exchange of information among systems, that are "open" to one another for this purpose by virtue of their mutual use of the applicable standards. Thus, the open-system interconnection environment is an abstract representation of the set of concepts, elements, functions, services, protocols etc. and is defined by a OSI-reference model and the derived specific standards, which, when applied to the configuration in FIG. 4, enable communications among the open systems A, B, C, S.
In the concept of OSI, a real system is a set of one or more computers, associated software, peripherals, terminals, human operators, physical processes, information transfer means etc. that forms an autonomous unit capable of performing information processing and/or information transfer. The "application process" is an element within a real open system, which performs the information processing for a particular application and some examples of application processes which are applicable to the open system definition are a FORTRAN program executing in a computer center and accessing a remote database or a process control program executing in a dedicated computer attached to some industrial equipment. Furthermore, as is shown in FIG. 4, the physical media for open systems interconnection provides the means for the transfer of information between the open systems.
To allow an interconnection of the real open systems, use is made of abstract models, which, however, find their equivalent in hardware or software realizations. A widespread standard is the OSI RM-international standards--organization open systems interconnection reference model--, which uses a layered architecture for interconnection as is shown in FIG. 5.
As is seen in FIG. 5, the concept of layering in cooperating open systems is based on the idea of introducing several communication layers from the physical media, wherein the highest layer is provided for interconnecting to a running application. Thus, each layer, which interconnects specific entities (services) of the respective open systems may be regarded as a "layer communication means". As is seen in FIG. 6, the individual entities within one layer communicate via the use of the (N)-protocol.
Thus, in such conventional data-communication systems, the communication requirements from the application into data streams in the lower layers is translated. In this translation process, each layer inserts a specific portion of intelligence which is specific to this layer's functionality.
Since data communication in advanced environments does include transfer over wireless systems and furthermore, system integration efforts lead to a decoupling of actual bearer capabilities and higher abstract (data) communication services, it will soon be common to use various networks for various data transmission services of one application simultaneously. It is obvious that the layered architecture described above is particularly advantageous, since the focus is on seamless roaming without the need to give the end-user any feedback about the actual used transmission media.
FIG. 7 shows an architecture with seven layers on top of the physical media. As aforesaid, within each layer, the "layer communication means" uses layer-specific parameters for the exchange of information to its peer-layer. Such layer-specific parameters are e.g. single transmission related parameters, such as the expected transmission delay, probability of corruption, probability of loss or duplication, probability of wrong delivery, cost, protection from unauthorized access and priority, multiple transmission related parameters like the expected throughput and the probability of out-of-sequence delivery or connection-mode parameters such as connection establishment delay, connection establishment failure probability, connection release delay, connection release failure probability and connection resilients. Such layer-specific parameters may be summarized as "quality of service (QOS) parameters".
Since the layered architecture of transmission protocols is structured in a top-down way, service access points SAP (a service access interface) are needed to request/use a service from a layer of the next lower order by the layer on top of it. The lower order layer then provides the service to the layer of higher order. FIG. 8 shows such service access interfaces between two layers N, N+1 to interconnect the respective entities in the layers. Here, the service access interfaces may connect entities which lie in the same open system or in fact in two different open systems.
As is further shown in FIG. 10, 11, the current architecture uses the service access interfaces SAP between two layers in order to request a service through the services access interface, whilst the lower layer provides the service to the higher layer. In order to establish communication within each layer (or in each layer communication means), the layer-specific parameters are used. In FIG. 10, the individual layers are illustrated as rectangular blocks, however, it should be understood that they comprise the configuration of FIG. 7, i.e. the exchange of information between two open systems A, B via the use of protocols and the layer-specific parameters.